The constellation of Orion is one of the most striking patterns of stars in the night sky. It is visible from both the northern and southern hemispheres, and there are few civilizations who haven’t recognised the seven primary stars as a coherent group. At whatever depth Orion is examined, it reveals fascinating astronomy, and a cultural significance that spans the globe and thousands of years of history.
Orion is named after the ancient Greek interpretation of the formation. Orion was a hunter, stung to death by a scorpion. The gods placed Orion and Scorpius opposite one another in the night sky and they chase each other across the heavens to this day. While people laugh at the imaginative interpretations of the constellations, most people are able to see the figure of Orion, even if they can’t see what his arms are doing. In the northern hemisphere, Orion stands fairly upright, and it should be easy to distinguish both of his shoulders, his famous belt, and his legs.
His left shoulder is the star Betelgeuse, a red supergiant. It’s one of only five red giants that are realistically visible to the naked eye. The supergiant label is well deserved; Betelgeuse is simply enormous and observational estimates suggest that its surface would significantly overlap the orbit of Mars were it to replace our own sun! The red hue is noticeable if the star is examined through binoculars. The reason Betelgeuse burns red is because it is an old star and running out of fuel. It is expected to explode in a supernova in the cosmically near future - some time in the next million years or so.
Opposite Betelgeuse, on the right shoulder is Bellatrix, literally ‘female warrior’ and also referred to as the Amazon star. The right knee, the brightest star in the constellation and the sixth brightest in the entire sky, is Rigel. Rigel is only one tenth the size of Betelgeuse, and is a similar distance from earth - around 700 light years. It is brighter in the sky because it is a fast burning blue supergiant. Temperatures on the surface can reach 11,000K, compared with 6,000K for our own sun.
The lower left knee is called Saiph. Once again, it is a similar distance from the earth to Rigel and Betelgeuse. It’s surface temperature is even higher than Rigel, at 26,000K, which means most of its emissions are in the ultraviolet region of the electromagnetic spectrum. This makes it dimmer in the visual range.
The last three of Orion’s main stars make up his belt. Named Alnitak, Alnilam and Mintaka, these stars are also referred to as the three kings. Just below Alnitak lie two beautiful nebulae - the flame nebula and the horsehead nebula - which are lit by the nearby star. It is said that they can be seen with good binoculars on a good night, but a telescope is probably required to pick them out.
Those seven stars are not the end of Orion’s treasures. Every hunter needs a weapon, and fastened to his belt, Orion has a sword. A group of stars hang in a vertical line from the belt... except one of them isn’t actually a star. Even with the naked eye, the Orion nebula appears as a blur rather than a point of late, and with binoculars, the wispy nature of the nebula becomes clear. This nebula, and the flame and horsehead nebulae, make up part of the Orion Molecular Cloud Complex. These regions are known as ‘stellar nurseries’ due to the high rate of star formation occurring within.
Orion also contains a number of stars above the left shoulder, and to the right of the body. The stars to the left are usually interpreted as Orion’s raised arm, holding a club. The stars to the right are seen to some as a shield or protective animal pelt, and to others as a wild beast which Orion is preparing to kill.
It is an interesting feature of Orion’s mythology that it is often associated with hunting stories, even in civilizations which had no contact with one another. In Australian aboriginal mythology, Orion’s body is a canoe, and his belt is a pair of fishermen and their catch. In some southern African mythologies, the body is a valley and the belt is a group of three antelope crossing from one side to the other. The sword is no longer a sword, but an arrow, fired by one of the ancestral hunters.
For the newcomer to astronomy, Orion is an easy and interesting constellation to start with, and even for seasoned stargazers it contains many treasures. The slow movement of the stars created Orion in its current form about two million years ago, making it one of the oldest recognisable constellations. It has existed alongside the human race ever since we climbed down from the treetops, and will remain one of the wonders of the sky for another two million years... as long as a supernova doesn't spoil the view!